The present invention relates to an inductor to be used in microwave integrated circuits, in particular an inductor being formed by a microstrip line.
In transmission paths in microwave integrated circuits, there is a need for various components such as inductors. In particular, there may be a need for an inductor, the characteristics of which can be varied, such as an inductor which can be switched between two inductance values as controlled by an electrical signal.
In Japanese patent application JP 2/101801, a microwave band-rejection filter is disclosed having transmission lines designed as linear microstrip, metal elements placed on top of an area of a layer of superconducting material. The superconducting material area has a pattern substantially agreeing with that of the metal conductor, except in some regions where the width of the superconducting area is larger than that of the metal conductor. When the superconducting material is in a non-superconducting state, most of the electric current passes through the common metal material of the metal conductor, whereas, in superconducting state, the electrical current passes only through the superconducting underlying material. The microstrip metal elements thereby obtain a variable filtering effect. However, a disadvantage of this design resides in providing a region having some, though it may be low, electrical conductivity placed under the normal conductor, since this region causes losses in the transmission line. The conductivity of materials, which are superconducting at a low temperature and are suitable for microwave integrated circuits, have in their normal state an electrical conductivity corresponding to some 10xe2x88x923 to 10xe2x88x922 times that of the electrical conductivity of the material of the always normal metal conductor.
It is an object of the invention to provide an electrical inductor of the microstrip type for microwaves exhibiting low losses.
An inductor for primarily microwave frequencies is constructed of a transmission line designed as a linear microstrip element made of a central line comprising normal electrically conducting material, such as a suitable metal. The microstrip element has a width which is varied by making areas at the sides of the central line superconducting. By changing the effective width of the microstrip, the inductance thereof is changed accordingly. The areas at the sides of the microstrip element are electrically connected along at least portions of the sides or of the edges of the central metal conductor. These superconducting areas, in their non-superconducting state, have some electrical conductivity which can be rather low. However, because they contact the central metal conductor only at a very low, thin or narrow edge, instead of contacting it at a large surface, they do not significantly affect the transmission characteristics of the transmission path when the superconducting areas are in the normal, not superconducting state.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the example and non-limiting methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.